NEMI Method Summary

Method Summary Information

Method Number: 8048 Media: WATER
Revision: Revised 1999; USEPA Accepted:  May 1, 1999
Method Source: Hach Company
Subcategory: INORGANIC Analytes in this method
Official Name: Phosphorous, Reactive - Ascorbic Acid Method
Descriptive Name Orthophosphate by Colorimetry
Source Info: Hach Company
P.O. Box 389
Loveland, Colorado, 80539-0389
phone: 800-227-4224
fax: 970-669-2932
Citation: 1997 Edition of the Hach Water Analysis Handbook
 
Brief Method
Summary:
 Ammonium molybdate and antimony potassium tartrate react in an acid medium (potassium pyrosulfate) with dilute solutions of phosphorus to form a yellow colored antimony-phospho-molybdate complex. This complex is reduced to an intensely blue-colored (molybdenum blue) complex by ascorbic acid. This color is proportional to the phosphorus concentration. All reagents for this reaction are contained in PhosVer 3 Phosphate Reagent.
Scope And
Application:
 Applicable to water, wastewater and seawater.
Applicable
Conc Range:
 0 - 5.0 mg/L Phosphate (1.7 mg/L as Phosphorous)
Interferences: Arsenate reacts with the molybdate reagent to produce a blue color similar to that formed with phosphate. Concentrations as low as 0.1 mg/L as interfere with the phosphate determination.
Sulfide (Na2S) and silicate do not interfere at concentrations of 1.0 and 10.0 mg/L, respectively.
Hexavalent chromium and NO2- interfere to give results about 3% low at concentrations of 1 mg/L and 10 to 15% low at concentrations of 10 mg/L.
Large amounts of turbidity may cause inconsistent results in the phosphate tests because the acid present in the powder pillow may dissolve some of the suspended particles and because of variable desorption of orthophosphate from the particles. For highly turbid or colored samples, add the contents of one Phosphate Pretreatment Powder Pillow to 25 mL of sample. Mix well. Use this solution to zero the instrument.
QC Requirements: Analysis of standards for accuracy check. Also, the Hach Water Handbook contains a general discussion of QC practices.
Sample Handling: If prompt analysis is impossible, preserve samples by filtering immediately and storing the sample at 4oC for a maximum holding time of 48 hours in either plastic or glass.
Max Holding Time:
 48 hours.
 
Relative Cost: Less than $50
URL to obtain ordering information for this method:
http://www.hach.com/products.htm
4828
Page 1